The present invention relates to ring pellets for gas generators having a central ignition channel. Such pellets serve for the production of gases or gaseous mixtures as utilized, for example, in airbags for automotive vehicles.
Ring pellets having a central, axially symmetrical middle channel have been disclosed in DE 3,416,736-C2. Nubs (called extensions therein) are arranged on the topside and underside of these pellets, the outer diameter of these nubs being smaller than the outer diameter of the entire pellet. These pellets are utilized in propellant charge igniters where they are arranged in an igniter tube, stacked one on top of the other to form a column. The arrangement of the nubs has the result that a free space is created between an inner wall of the igniter tube and the pellet, preventing the formation of an undesirable pressure buildup within the igniter tube.
However, the ring pellets described in DE 3,416,736-C2 are not suitable for use in gas generators since the pellets described in the reference develop hot gases serving for the ignition of the propellant charge surrounding the igniter tube. In contrast thereto, ring pellets for gas generators are to deliver maximally cool gases so that the problems playing a large part in case of pellets for propellant charge igniters are of subordinate importance in these pellets. For this reason, ring pellets for gas generators are disclosed in DE 3,742,656-Al wherein the nubs are arranged only within a small annular region on the topside and underside of the pellets so that these nubs are not flush with the rim of the pellet at any point. In accordance with statements made in this patent, this arrangement permits a quick deflagration of the pellets. However, it has been found that with this type of pellet design, the gas conductance of the vapors produced during the combustion of the pellets is not at an optimum so that these pellets frequently show inadequate reaction rates.
Therefore, the problem was to be solved of developing pellets for gas generators which, when arranged into a stack, combust quickly in a readily controllable fashion, and the vapors of which are rapidly exhausted or discharged.